To answer the original question, I have an e-Machines EtherDock which works with my Duo 2300c. It works for file transfers and internet (as much as internet can be said to work with OS 8.0 and Netscape Communicator 4.08.)

I have a second EtherDock which works when the moon is in the second house or some other requirement I haven't yet pinned down. xx( Some days it is bulletproof. Some days it can't make an ethernet link.